Recording sheets

ABSTRACT

The recording sheet is formed by coating colored sheets with an opacifying compound prepared by mixing an aqueous suspension of polymer particles embodying internal voids dispersed with a water base coating material.

TECHNICAL FIELD

The present invention relates to coated sheets for use in graphicallyrecording the output of tachographs (recording tachographs), dusk meters(electrocardiographs), and other measuring instruments and, moreparticularly, to a recording paper printable with an inkless recordingpen (stylus).

BACKGROUND ART

Recording paper, printable with a stylus, is made by forming an opaquelayer on a colored substrate. The printing effect is achieved either byremoving or by imparting a light transparency to portions of the opaquelayer by contact with the stylus. Various types of recording papers areknown in the art.

Those papers on which the recording is made by scraping the stylus overthe opaque layer are made by applying a lacquer containing film formingcomponents such as nitrocellulose or cellulose acetate on ablack-colored paper and opacifying the coating (e.g., Japanese PublishedPatent Publication Nos. 34-8163 and 41-19274); or by applying a whitecoating containing titanium dioxide pigment or the like on ablack-colored paper (e.g., Japanese Published Utility Model PublicationNo. 39-33446). Local scraping of the surface removes the coating anddiscloses the underlying black surface, the stylus being moved inresponse to an electrical signal.

For those papers to which transparency is to be imparted by the stylus,a light diffusion layer and a layer embodying solvent containingcapsules are deposited on a colored paper substrate (Japanese Patent No.520631). With this type of recording paper the recording is made bybreaking the capsules with the stylus (moved in response to anelectrical signal), resulting in releasing the solvents to permeate intothe light diffusion layer. Thus, the light diffusion layer is madelocally transparent and the underlying color of the colored substrate isdisclosed.

Among the former processes, the recording paper using lacquers employlow boiling point solvents such as ketones (for example, acetone),alcohols (for example, methanol) or the like to dissolve the filmforming components such as nitrocellulose or cellulose acetate.Obviously, the risk of fire and explosion are great hazards in thecoating process. These components are also detrimental to the workingenvironment as the solvents evaporate into the air. Another difficultyinherent in this process is that the lacquer coating must be subjectedto a prolonged period of drying at a low temperature or a mild heatingunder an optimum humidity to obtain the required whitening effect. Thissituation is quite adverse to the improvement of productivity. Also, therecording paper that is prepared by applying a white coating has a poorappearance due to a resultant coarse surface and is deficient in printdefinition and printability.

The recording paper made by the latter process (i.e. requiring definitebreakage of capsules by a stylus) involves the problem of slow printingspeed and subsequent poor storage stability owing to the discolorationof the printed sheet.

U.S. Pat. No. 2,739,909 discloses a process by which a lacquer mixtureis prepared by first introducing a W/O (water-in-oil) type emulsifierinto a resinous organic solution in which PMMA is dissolved. Thereafter,water is added under agitation to disperse micron size water dropletstherein. The recording paper is subsequently prepared by applying themixture on the colored substrate which is then dried. According to theU.S. Patent, the solvents first evaporate in the drying process, and acoating film of PMMA which embodies the dispersed water droplets thereinis formed. Then, when water in the droplets evaporates, the white opaquelayer is formed in which voids are left in the polymer coating film.

In this case again, the polymer solution contains a large amount ofsolvent and does not contribute to solving the problem of fire andexplosion hazards and deterioration of the working environment similarto the process using lacquers.

DISCLOSURE OF THE INVENTION

An object of this invention is to obtain commercially usable recordingsheets, which can be produced under a safe condition and at a highlyefficient level of productivity. As illustrated generally in FIGS. 1 and2, the recording paper 7 is made by applying an opacifying compound oncolored substrates 2, 5, respectively, to form opaque layers 6. Theopacifying compound is prepared by mixing an aqueous suspension, inwhich polymer particles 8 embodying voids therein are dispersed, with awater base polymeric film forming vehicle. A solution or dispersion of afilm forming component which uses water as a solvent or as a dispersingmedium, also fits this definition as is described hereinafter. In thepresent description, the terminology, "aqueous opacifying compound" asused means an opacifying compound using water as a solvent.

The color substrates 2 and 5 are paper, synthetic paper, or plasticfilms and may be colored with inks, pigments, dyestuffs or the like,either by means of impregnating or kneading the coloring material intothe substrate when formed (substrate 2 in FIG. 1) or by subsequentlycoating the substrates with a layer of coloring material (substrate 5 inFIG. 2). Coloring materials such as inks, pigments, dyestuffs and thelike are usually black in color, but coloring materials of other colorssuch as red or the like may be used.

Plastic films such as polyester film, polyvinylchloride film,polyvinylidene chloride film, poly (meta) acrylate ester film,polycarbonate film, polyethylene film, polypropylene film, etc., can beused for the substrate.

Polymer particles (particles 8 as seen in FIGS. 1 and 2) embodying voidstherein are disclosed in Japanese Laid-Open Patent Publications Nos.56-32513, 60-69103, 60-223873, 61-87734, 61-185505, 62-127336,63-110208, 63-135409, 63-213509, and are now commercially available onthe market under the product names such as Ropaque OP-42, OP-62(manufactured by Rohm and Haas Co., Ltd.), Ropaque OP-84J (manufacturedby Japan Acrylic Chemical Co., Ltd.), Voncoat PP-1000, PP-1001S, PP-2000and PP-1100 (manufactured by Dainippon Ink & Chemicals, Inc.),JSRSX-862(A) and SX-850(B) (manufactured by Japan Synthetic Rubber Co.,Ltd.), and Expancel WU#642 (manufactured by Expancel Corp. and KemanobelCorp., Sweden). It is desirable that the particle product has a corecomponent (core) comprising a homopolymer or copolymer of methacrylicacid and a sheathing component (shell) comprising homopolymer orcopolymer of styrene monomer.

In manufacturing the particles, the following known processes may beused: (I) incorporation of a blowing agent in the polymer particles andforcing the blowing agent to expand; (II) enclosure of a volatilecomponent such as butane or the like in the polymers and forcing thebutane to expand by gasification under increased temperature; (III)enclosure of a gas into melted polymers by blowing thereon a jet of airor gas, etc.; (IV) embodiment of alkali swellable substance such ascarboxylic acid polymer or the like inside the polymer particles andcausing its expansion by the addition of alkalis; (V) preparation ofW/O/W (water-in-hydrophobic-monomer-in water) type monomer emulsions andpolymerization thereof, (VI) embodiment of acid swellable polymers, suchas amine polymers or the like, in the polymer particles and causingtheir expansion by the addition of acids; (VII) formation of voids byembodiment of hydrophobic solvents such as toluene, hexane and so on inthe polymer particles; (VIII) two stage crosslinking of polymers ofdifferent compatibility on seeds comprising crosslinked polymerparticles; (IX) polymerization shrinkage of polymers, and so on.

The diameter of the polymer particles 8 may be in the range of 0.01 to50 microns, and preferably should be 0.1 tip 5 microns. Polymerparticles made by the aforementioned processes possess a high opacifyingpower as the core component of each particle contains aerated voids.

An aqueous suspension is prepared by dispersing the above-mentionedpolymer particles in water and thereafter mixed with a water basepolymeric film forming vehicle to make the opacifying compound. Thewater base vehicle is an aqueous dispersion or solution of a coatingfilm forming component synthesized by emulsion polymerization orsolution polymerization or the like and is supplied in such forms as anaqueous solution, emulsion and aqueous dispersion. For the coating filmforming component, polymer synthesized by homopolymerization orcopolymerization of such monomers as acrylic esters, methacrylic esters,styrene, butadiene, chloroprene, vinylidene, vinyl acetate, etc. can beused. Also, natural or synthesized ruffer latex can be used. Polymersare modified so that they will have a glass transition temperature (Tg)of not over 100° C., preferably between -22° C. to 25° C.

A water base polymeric film forming vehicle in the form of an aqueousdispersion or an emulsion is prepared by dispersion polymers synthesizedby homopolymerization of such monomers as ethyl acrylate (EA),butylacrylate (BA), 2 ethylhexylacrylate (2EHA) and butadiene or bycopolymerization of these main monomers with methylmethacrylate (MMA),styrene (ST) or vinylacetate etc.

A water soluble type water base polymeric film forming vehicle may alsobe a polymer prepared by homopolymerization or copolymerization of theaforementioned monomers, which are partially substituted with acarboxylic group, amino group or amide group and dissolved in water inthe form of alkali salt or acid salt or as is. Examples of monomers withcarboxylic groups are acrylic acid (Aa), methacrylic acid (Maa),monomethylitaconic acid (MMI), 2-carboxyethyl acrylic ester, etc. Thosewith an amino group may be N, N'-dimethylaminoethyl acrylate, allylamine, etc. and those with an amide group are (meta) acrylamide. Thepolymers are dissolved in water by transforming carboxylic acid intosalts of alkali metals, amines or ammonia and amino group into salts ofhydrochloric acid or acetic acid. If necessary, plasticizers (forexample, dibutyl phthalate, polybutene etc.), wetting agents (forexample, ethylene glycol, propylene glycol, anionic surfactants,nonionic surfactants etc.), defoamers, thickeners (e.g.,hydroxyethylcellulose, sodium polyacrylate, polyvinyl alcohol, etc.),aqueous water wax emulsions (e.g., carnauba wax, polyethylene wax,paraffin wax, chlorinated paraffin wax, etc.) may be added.

The above suspensions and water base polymeric film forming vehicles aremixed arbitrarily in a ratio of between 1:9 and 9:1, the preferred ratiobeing between 1:3 and 6:1.

The opacifying compound thus prepared is uniformly applied on thecolored substrates by an airknife coater, a roll coater, spraying or thelike and controlled to keep the final thickness of the opacifying layer6, after drying by heated air (between 50° to 200° C.), between 1 and 20microns, and preferably between 3 and 10 microns. As shown in FIG. 5,the obtained opaque layer 6 has such a structure that the polymerparticles 8, embodying voids therein, are bound by the coating filmforming component of the water base vehicle to the substrate after theevaporation of water and the layer completely hides the color of thecolored substrate (2 and 5) giving to the paper a normal whiteappearance.

The recording papers 7, constituted as described above, have a highhiding property because incident light is scattered by the voidsembodied in the core of polymer particles 8 in the opaque layer 6. Also,as the water base vehicle adheres the polymer particles 8 to thesubstrates 2 and 5, the opaque layer does not detach from the sheetsunder normal treatment, yet is easily removed or made transparent ortranslucent by inscription of a stylus 9. The polymer particles 8 aresupplied in a completely dispersed state in water, and as the opacifyingcompound is prepared by mixing this component with a water base vehicle,there is no danger of fire or explosion hazards in the coating processand no need to employ a whitening process.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings:

FIG. 1 is a cross sectional view of a recording paper prepared inaccordance with the present invention;

FIG. 2 is a cross sectional view of a recording paper prepared inaccordance with a second embodiment of the present invention;

FIG. 3 is a cross sectional view of a recording paper on which therecording is made by the inscription of a stylus;

FIG. 4 is a cross sectional view of a recording paper where therecording is made by obtaining transparency or translucency throughcompressive inscription of a stylus; and

FIG. 5 is a schematic cross sectional view showing the structure of theopaque layer of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will hereinafter be described indetail with reference to the accompanying drawings.

A) Preparation of a colored substrate

As seen in FIG. 1, a high quality paper 2 (manufactured by Oji PaperCo., Ltd., having an area weight of about 150 g/m²) was coated with ablack ink, based on a carbon black dispersion, at the rate of 4 gsolids/m² and then dried, thereby obtaining a black colored substrate 2.Also, a black ink was prepared by mixing 50 parts of a commerciallyavailable aqueous black ink (manufactured by Dainippon Ink & Chemicals,Inc., under the product name DICSAF BAG-C805 black) with 50 parts of anacrylic emulsion polymer (copolymer of MMA-Ba-Maa with Tg of -3° C.).Then, this black ink was applied on a polyester film 3 (manufactured byToyobo Co., Ltd., at a thickness of about 100 microns) by a wire rod barapplicator No. 8 thereby to obtain a black substrate 5 on which a blackcoating film 4 was formed.

B) Preparation of the opacifying compounds

Water base opacifying compounds (Table 1) were obtained by mixing theopacifying components with film forming components (sample Nos. 1through 5, (sample No. 5 is the control reference).

                  TABLE 1                                                         ______________________________________                                                  Sample Nos.                                                                     1    2        3      4      5                                     ______________________________________                                        opacifying                                                                    component                                                                     Ropaque OP-62 25                                                              Voncoat PP-1000      25                                                       Ropaque OP-42                 25                                              Ropaque OP-85J                     25                                         Ti-Pure P-610                             25                                  film forming                                                                  component                                                                     acryl emulsion                                                                              12.5                                                            polymer                                                                       SBR 0629             12.5                                                     Nikasol TS-662                12.5                                            water solluble                     12.5                                       acrylic polymer                                                               Pegar LV-19                               12.5                                water         20     20            30     30                                  auxiliary                                                                     agent                                                                         Fluorad FC-149                                                                              0.5                                                             chlorinated                                                                   paraffin wax                  4                                               Nopcosant K                               6                                   Triton CF-10                              0.5                                 ______________________________________                                    

In Table 1 the opacifying component Ropaque is a polymer particleproduct made by Rohm and Haas Co., with a solids content of grade OP-62,37.5%, grade OP-42, 40.0%. Ropaque OP-85J is a product of the JapanAcrylic Chemical Co., Ltd. and has a solids content of 42.5%. VoncoatPP-1000 is a polymer particles product of Dainippon Ink & Chemicals,Inc., with a solids content of 45%. Ti-Pure P-610 is a powder oftitanium dioxide produced by E.I. du Pont de Nemours & Company but isnot a polymer particle product.

The acrylic emulsion polymer in the film forming component is acopolymer of BA and Maa in the ratio of 97:3 and has a Tg of -50.5° C.with a solids content of 45%. SBR 0629 is a product of Japan SyntheticRubber Co., Ltd., and is essentially a styrene butadiene latex. NikasolTS-662 is an adhering type acrylic emulsion polymer manufactured byNippon Carbide Industries Co., Inc. A water soluble acrylic polymercomprises EA and monomethylitaconic ester in the ratio of 80:20, has anaverage molecular weight of 10,000 with a solid content of 30% and issupplied as an ammonium salt aqueous solution. Pegar LV-19, a product ofKoatsu Gas Kogyo Co., Ltd., is an acrylic emulsion polymer foradhesives, having a solids content of 55.5%.

Auxiliary agent, Fluorad FC-149 is a product of Sumitomo 3M Co., and isan aqueous solution with a 1% active ingredient. Chlorinated paraffinwax is an aqueous emulsion with a 40% solids content. Nopcosant K is adispersion agent based on sodium polyacrylate manufactured by San NopcoCo. Ltd. Triton CF-10 is a nonionic surfactant supplied by Rohm and HaasCompany.

C) Preparation of recording paper

The recording paper 7 (sample Nos. 6 through 10, sample No. 10 being forreference data) was prepared by applying the opacifying compounds(sample Nos. 1 through 5) on the black substrate 5 of FIG. 2 by the wirerod bar applicator No. 12 and drying the opacifying compounds at 50° C.for 30 minutes to provide the opaque layer 6 having a thickness of about5 microns. Also, the recording paper 7 (sample No. 8a) was prepared byapplying the opacifying compound (sample No. 3) on the black coloredsubstrate 5 of FIG. 2 by the wire rod bar applicator No. 12 and dryingthe same at 50° C. for 30 minutes to provide the opaque layer 6 having athickness of about 5 microns. In the drawing, reference numeral 8depicts the scattered state of polymer particles in the opacifying layer6.

D) Recording tests

The recording paper 7 (sample Nos. 6 through 10) thus prepared weremounted on a tachograph, and the recording was performed by theinscription with a sapphire needle 9 (see FIGS. 3 and 4). The inscribedrecording sheets were taken out and evaluated for such properties aswhiteness (visual observation of surface whiteness), appearance (visualobservation of surface smoothness), print definition (visual observationof print clearness) and printability (press an adhesive tape on theopaque layer and pull the same to observe the layer's resistance todelamination) using as a standard the commercially available tachographrecording paper (manufactured by Yazaki Sogyo Co., Ltd., where theopaque layer was prepared by applying lacquer coating based on solventsolution of cellulose acetate and nitrocellulose). Evaluation resultsare shown on Table 2.

                  TABLE 2                                                         ______________________________________                                                Sample Nos.                                                                                                10 (reference                                    6    7      8      8a   9    data)                                    ______________________________________                                        whiteness ⊚                                                                     Δ                                                                              Δ                                                                            Δ                                                                            ◯                                                                      ⊚                       appearance                                                                              ◯                                                                        ◯                                                                        ◯                                                                      ◯                                                                      ◯                                                                      X                                      print     ◯                                                                        Δ                                                                              ◯                                                                      ◯                                                                      ◯                                                                      X                                      definition                                                                    printability                                                                            ◯                                                                        ◯                                                                        Δ                                                                            ◯                                                                      ◯                                                                      X                                      ______________________________________                                    

In Table 2, ⊚ denotes better than commercial product, ∘ denotes equal tocommercial product, .increment. denotes inferiority to commercialproduct but usable, and X denotes remarkable inferiority to commercialproduct and not usable.

Table 2 demonstrates that Sample Nos. 6 and 9 exhibited performanceequal to or better than the commercially available tachograph recordingpaper. Sample Nos. 7, 8 and 8a are appreciably lower in whiteness butare suitable for commercial in respect of appearance, print definitionand printability.

As described above, the recording paper of the present invention isprepared by using the water base opacifying compounds, and there is norisk of fire and ignition in the manufacturing process. Therefore, theprocess of the present invention is safe. Further, since the whiteningprocess is eliminated, the efficiency of productivity can be improved.Furthermore, it is possible to provide the recording papers which havean appearance, print definition and printability equal to those of theconventional recording sheet.

INDUSTRIAL APPLICABILITY

As described above, the recording sheet according to the presentinvention is suitable for use on a tachograph, a dusk meter and othermeasuring instruments and useful for recording the changes of rotationalspeed and electrical current or potential in a semipermanent quality.

What is claimed is:
 1. Recording paper comprising a colored substratecoated on at least on surface with an opaque layer comprising a mixturein a ratio of between 1:9 and 9:1, respectively, of an aqueoussuspension opacifying polymer particles having voids therein and apolymeric film forming vehicle, said mixture being uniformly applied tosaid substrate and thereafter dried.
 2. The recording paper according toclaim 1, wherein said opacifying polymer particles have a core componentsynthesized by homopolymerization or copolymerization of a methacrylicacid and a sheathing component synthesized by homopolymerization orcopolymerization of a styrene monomer, said opacifying polymer particleshaving a diameter of 0.1 to 5 microns.
 3. The recording paper accordingto claim 1 or 2, wherein the polymeric film forming vehicle has a glasstransition temperature (Tg) of not higher than 100° C.
 4. The recordingpaper according to claim 3, wherein the aqueous suspension and thepolymeric film forming vehicle are mixed in the ratio of between 1:3 and6:1.
 5. The recording sheet according to claim 4, wherein saidopacifying layer has a thickness of 1 to 20 microns.
 6. A method offorming recording papers, comprising the steps of preparing a uniformdispersion in a ratio of between 1:9 and 9:1, respectively, of anaqueous suspension of polymer particles having voids therein and anaqueous polymeric film forming vehicle, uniformly coating a surface of acolored sheet substrate with said suspension and thereafter drying saidcoated substrate.
 7. The method according to claim 6, including the stepof forming said polymer particles with a core component synthesized bythe polymerization of methacrylic acid and a shell component synthesizedby the polymerization of a styrene monomer and said polymer particlebeing of a diameter of between 0.1 and 5 microns.
 8. The methodaccording to claim 7, wherein the glass transition temperature (Tg) ofsaid shell component is less than 100° C.
 9. The method according toclaim 6, wherein the suspension of polymeric particles and the polymericfilm forming vehicle are mixed in the ratio of between 1:3 and 6:1.